Karimata Strait

The Karimata Strait (Indonesian: Selat Karimata) also spelled Carimata[1] or Caramata[2] is the wide strait that connects the South China Sea to the Java Sea, separating the Indonesian islands of Sumatra and Borneo (Kalimantan). It is bordered by the Belitung island (off Sumatra's eastern coast) in the west and Borneo in the east. It is the widest strait that connects the South China Sea and the Java Sea (other straits include the Bangka and Gaspar Straits), but its numerous islands and reefs reduce its navigability. Its weather and current is influenced by the annual southeast and northwest monsoon.

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The strait is about 125 miles (109 nmi; 201 km) wide from the east coast of Belitung (also known as Billiton) to the west coast of Borneo (Kalimantan).[3] The much narrower Gaspar Strait separates Belitung from Bangka Island to the west.[4] Bangka lies close to the east coast of Sumatra, separated from it by the Bangka Strait.[5] To the east of Belitung lie reefs and a group of islets known as the Montaran Islands, extending up to 40 nautical miles (46 mi; 74 km) from Belitung's northeastern coast.[6] The Karimata Islands lie in the eastern part of the Karimata strait, northeast of Belitung, southwest of Maja Island and off-shore from the west coast of Borneo.[1] The presence of these islands and reefs reduce the width of the main navigable channel to about 45 nautical miles (52 mi; 83 km).[1] Outside this main fairway, there are multiple navigable channels to the east of Karimata Islands or between the islands.[7]

The southeast monsoon prevails in the strait from about the end of May, which comes with strong southeast or south-southeast wind, a dry weather, and mist that can obscure visibility. The northwest monsoon comes from the beginning of October, characterized by thunderstorms, rain and squalls alternating with calm days with fair weather. The biggest rainfall occur from November to February. From February, the weather becomes unpredictable because of the changing monsoon, before settling again around the end of May.[9]

The current strength of the strait vary depending on the monsoon wind. At the peak of either monsoon, the current can run up to 3 miles per hour. When the monsoon is light, "there is little or no current" and the direction may be subject to the tidal stream.[10]

The strait's currents run between the South China Sea to its north and the Java Sea to its south.[11] Since it is relatively shallow, with the depth of 50 metres (160 ft) or less, the volume transported by the current is relatively small.[12] A 2007–2008 study by a group of Indonesian and Chinese researchers found that the transport volume averaged 0.5 m3/second (or 0.5 Sv) with a net southward direction (i.e. to the Java Sea).[13] During the northern hemisphere winter, roughly during the northwest monsoon, water flowed southward averaging 2.7 Sv.[13] The flow was reversed during the northern hemisphere summer, roughly during the southwest monsoon, with an average transport of 1.2 Sv.[13]

It was known to British sailors in the 18th and 19th centuries as the Caramata Passage. The strait was used as a route by the British fleet for its Invasion of Java (1811), sailing from the British base in Malacca to the island of Java, then part of the Dutch East Indies.[2] Initially, the British were unsure of the strait's practicability, and hesitated between taking it or a northeast passage around the north of Borneo and through Makassar Strait.[14] A report by Sir Thomas Stamford Raffles, then a British officer in Malacca, recommended taking the Karimata route, which he considered "less dangerous than tedious" than the northeast passage during that time of year.[15] Raffles estimated that this journey would take the British fleet between a month and six weeks for "the fleet sailing in divisions".[15] The British Governor-General of IndiaThe Lord Minto decided to take Raffles's suggestion over the objection of some naval officers.[16] The fleet, numbering about 100 vessels and transporting about 11,000 troops, departed Malacca between 11 and 18 June 1811,[17] and reached the coast of Java on 30 July after a smooth journey, exactly six weeks after Minto and Raffles' departure.[18]

A 1915 publication by the United States Hydrographic Office commented that despite being much wider, the strait did not have as much traffic as the parallel Bangka or Gaspar Straits. The publication said that the advantage of its breadth was often outweighed by the danger posed by shoals in the strait, as well as its more irregular currents.[1]